The present invention relates to a driver device which causes a vibrator to produce driving vibrations, a physical quantity measuring device (e.g. vibrating gyroscope) using the driver device, and an electronic instrument.
Gyroscopes are classified as a rotating gyroscope, a vibrating gyroscope, and the like depending on the method of detecting the force applied to an object. In particular, the vibrating gyroscope is considered to be advantageous for reducing size and cost from the viewpoint of the constituent elements and the like. As a vibrating gyrosensor which detects an angular velocity applied to an object, a piezoelectric vibrating gyrosensor is known which excites a crystal or a piezoelectric element advantageous for increasing reliability and reducing size. The piezoelectric vibrating gyrosensor utilizes a phenomenon in which a Coriolis force occurs perpendicularly to vibrations when an angular velocity is applied to a vibrating object.
For example, a vibrating gyrosensor which detects an angular velocity causes a physical quantity transducer (vibrator) to produce driving vibrations in a specific direction. When an angular velocity is applied to the vibrator, a Coriolis force occurs perpendicularly to driving vibrations to produce detection vibrations. Since the detection vibrations occur perpendicularly to the driving vibrations, a detection signal (signal component due to detection vibrations) differs in phase from a driving signal (signal component due to driving vibrations) by 90 degrees. The detection signal can be synchronously detected separately from the driving signal utilizing the above phenomenon, for example.
A reduction in size and an increase in reliability of the vibrating gyrosensor can be achieved using a crystal vibrator.
The vibrating gyrosensor is used in a wide variety of applications, such as shake detection for a video camera or a digital camera, positioning using a global positioning system (GPS) for a car navigation system, and aircraft or robot position detection.
The vibrating gyrosensor used in these applications is driven by a battery. Therefore, it is necessary to increase the life of the battery by reducing the power consumption of the vibrating gyrosensor as much as possible. In this case, it is preferable to stop supplying power to the vibrating gyrosensor when an angular velocity or the like is not detected and to supply power to the vibrating gyrosensor from the battery only when using the vibrating gyrosensor. This makes it necessary to cause the vibrating gyrosensor to perform a normal operation within a short period of time after activation.
Specifically, it is important to cause the vibrating gyrosensor to promptly transition to an operation state in which the gyrosensor can detect a physical quantity (steady oscillation state) when supplying power (during oscillation startup). For example, when using a vibrator such as a crystal vibrator which has a high Q value and requires a long time until stable oscillations are achieved after supplying power, it is very difficult to achieve a high-speed transition to the steady oscillation state.
In order to reduce power consumption, it is preferable to suspend the operation of an unnecessary circuit when a physical quantity such as an angular velocity need not be detected. When providing a low power consumption mode (sleep mode), the circuit must be designed to enable a high-speed recovery from the low power consumption mode (sleep mode) to the normal operation mode.
JP-A-2004-286503 and JP-A-2003-240556 disclose technologies for reducing the startup time of such a vibrating gyrosensor, for example. JP-A-2004-286503 discloses technology in which a CR oscillation circuit or a ring oscillator is provided in an oscillation loop so that the oscillation amplitude is increased using an amplifier immediately after activation. JP-A-2003-240556 discloses technology in which a resistor is provided in series with a crystal vibrator to reduce the period of time until the signal from the vibrator is stabilized.
A vibrating gyrosensor driver device must cause the vibrator to constantly vibrate (oscillate) at a resonance frequency in order to stably detect the angular velocity applied to the vibrator. The driver device also must cause the vibrator to oscillate within a short time to start a normal operation. Furthermore, it is preferable to form the driver device using a small circuit with low power consumption in order to increase the life of the battery at low cost.
On the other hand, if the vibrator is formed of a crystal having a high Q value and is sealed in a package under vacuum, the driving Q value of the vibrator increases to a large extent. Therefore, the time (startup time) elapsed until the signal from the vibrator is stabilized increases when causing the vibrator to produce driving vibrations.
A sleep mode may be provided as the operation mode of the driver device aiming at reducing its power consumption so that the operation of the circuit is suspended when unnecessary and the normal operation is recovered quickly when necessary. In particular, when causing a crystal vibrator to oscillate, the oscillation startup time increases due to a high Q value. Therefore, it is necessary to at least cause the crystal vibrator to continuously oscillate in order to reduce the normal operation recovery time.
It is necessary to prevent mechanical destruction of the vibrator by controlling energy (current) for causing the vibrator to produce mechanical vibrations. However, when the operation of an unnecessary circuit is terminated in the sleep mode in order to reduce power consumption, the oscillation amplitude in the oscillation loop is not controlled. In this case, an excessive current may flow through the vibrator, whereby the vibrator may break. This causes the reliability of the gyrosensor to deteriorate. Therefore, it is necessary to provide a circuit which monitors a signal in the oscillation loop and to operate this circuit in the sleep mode.
According to the technology disclosed in JP-A-2004-286503, when causing the crystal vibrator to oscillate at a frequency close to its driving frequency, the areas of the capacitor and the resistor of the CR oscillation circuit must be increased. This results in an increase in size and cost of the vibrating gyroscope (vibrating gyrosensor). According to the technology disclosed in JP-A-2004-286503, it is difficult to cause the crystal oscillator with a high Q value to promptly operate at its driving frequency since the crystal oscillator is driven at another frequency during startup. Therefore, the period of time until stable oscillations are achieved increases when affected by a manufacturing variation and the like. Therefore, the technology disclosed in JP-A-2004-286503 results in an increase in startup time and power consumption, even if a sleep mode is provided.
According to the technology disclosed in JP-A-2003-240556, it is necessary to insert a resistor. In general, when incorporating a resistor in an integrated circuit device, it is difficult to provide the vibrator with desired energy due to a large manufacturing variation of the resistor. According to the technology disclosed in JP-A-2003-240556, a gain loss occurs since the energy applied to the vibrator is divided by the resistor. Therefore, the technology disclosed in JP-A-2003-240556 results in an increase in startup time and power consumption due to a gain loss, even if a sleep mode is provided. Even if the driver device is set in a sleep mode, power consumption increases when adjusting the level of the oscillation signal in order to prevent destruction of the vibrator.